High voltage transmission and distribution lines crisscross the country and bring electricity to homes and businesses from sea to shining sea. Occasionally, these electric power lines need to be taken out of service for some reason, such as testing, maintenance, upgrade, repair, and so forth. When taking the electric power lines out of service, a first end is opened, then the second end. When the first end has been opened and the second end is still at line voltage, the electric power line forms a large, geographic capacitor between the line conductors, at line potential, and ground. The charging current for a typical electric power line in this state is on the order of five to several hundred amperes, which represents a significant amount of stored energy when system voltage is on the order of 25 kV to 242 kV.
In order to completely disconnect a charged transmission line, the circuit must be opened through a circuit interrupter without causing a current flash-over to ground. This is typically performed with an air-arcing switch for a disconnect switch at certain voltages, an SF6 dielectric switch at intermediate voltages, and a circuit breaker at higher voltages. The arcing current has a tendency to restrike between current zero crossings as the voltage periodically alternates toward the maximum voltage while the circuit interrupter opens creating an increasing arc gap. As the circuit interrupter arc gap widens so does the magnitude of the current restrikes across the arc gap. The voltage build up across the arc gap correspondingly increases, which at a critical point causes the current to flash-over to ground if the circuit is not broken before the voltage across the arc gap reaches this critical point. High current restrikes degrade the circuit interrupter, and more importantly current flash-over events cause dangerous conditions at the substation and also injects voltage and current spikes back into the electric power system which can be potentially damaging to power system equipment and connected loads.
As a result the rating and operational capacity of the circuit interrupter is limited by its ability to break the circuit at a sufficiently low voltage build up across the arc gap to prevent a current flash-over. This corresponds directly to the number of current restrikes that occur before the circuit is broken because each successive restrike occurs across an increasing wide arc gap, corresponding in turn to an increasing large voltage across the arc gap. This is equivalent to saying that the longer the time to break the circuit, the larger the number of restrikes, and the greater the chance for flash-over. Thus, allowing the circuit interrupter to break the discharging circuit at a lower arc gap voltage than would occur without the current pause device, and thereby increases the current and voltage rating as well as the operational capability of the circuit interrupter.
Accordingly, there is an ongoing need for a cost effective circuit interrupters and associated devices that increase the current and voltage rating as well as the operational capability of circuit interrupters.